Method of manufacturing solar cell

ABSTRACT

Disclosed is a manufacturing method of a solar cell, including forming a photoelectric converter including an amorphous semiconductor layer, forming an electrode connected to the photoelectric converter, and performing a post-treatment by providing light to the photoelectric converter and the electrode.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the priority benefit of Korean PatentApplications No. 10-2015-0181748, filed on Dec. 18, 2015 and No.10-2016-0154395, filed on Nov. 18, 2016 in the Korean IntellectualProperty Office, all of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Embodiments of the present invention relate to a method of manufacturinga solar cell, and more particularly, to a method of manufacturing asolar cell including an amorphous semiconductor layer.

2. Description of the Related Art

Recently, due to depletion of existing energy resources, such as oil andcoal, interest in alternative sources of energy to replace the existingenergy resources is increasing. Most of all, solar cells are popularnext generation cells to convert sunlight into electrical energy.

Solar cells may be manufactured by forming various layers and electrodesbased on some design. The efficiency of solar cells may be determined bythe design of the various layers and electrodes. In order for solarcells to be commercialized, the problem of low efficiency needs to beovercome, and thus, various layers and electrodes are being designed tomaximize the efficiency of solar cells and various treatments are beingperformed with the goal of maximizing the efficiency of solar cells.

Accordingly, there is a demand for a method of manufacturing a solarcell, which includes a process of performing post-treatment on the solarcell so as to maximize the efficiency thereof based on the structure ofthe solar cell. In particular, there is a demand for a method ofmanufacturing a solar cell including an amorphous semiconductor layer,which may prevent deterioration of the amorphous semiconductor layer ata high temperature because the efficiency of the solar cell may bereduced by such deterioration of the amorphous semiconductor layer, orby implementation of a low-temperature process required to prevent thedeterioration of the amorphous semiconductor layer.

SUMMARY OF THE INVENTION

Therefore, the present invention has been made in view of the aboveproblems, and it is an object of the embodiments of the presentinvention to provide a method of manufacturing a solar cell, which mayenhance the thermal stability and efficiency of the solar cell.

According to an aspect of the present invention, the above and otherobjects can be accomplished by the provision of a method ofmanufacturing a solar cell, the method including forming a photoelectricconverter including an amorphous semiconductor layer, forming anelectrode connected to the photoelectric converter, and performing apost-treatment by providing light to the photoelectric converter and theelectrode.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and other advantages of theembodiments of the present invention will be more clearly understoodfrom the following detailed description taken in conjunction with theaccompanying drawings, in which:

FIG. 1 is a sectional view illustrating an example of a solar cell, towhich a method of manufacturing a solar cell according to an embodimentof the present invention may be applied;

FIG. 2 is a plan view of a second electrode layer in the solar cellillustrated in FIG. 1;

FIG. 3 is a flowchart illustrating a method of manufacturing a solarcell according to an embodiment of the present invention;

FIGS. 4A to 4I are sectional views illustrating the method ofmanufacturing the solar cell illustrated in FIG. 3;

FIG. 4J is a diagram for explaining a post-treatment operation includingtwo operations according to the present embodiment;

FIG. 5 is a view illustrating the results of measuring the temperatureof the solar cell (or a semiconductor substrate) in two respective casesin which only heat is applied and in which heat and light are appliedtogether, in a post-treatment operation of the method of manufacturingthe solar cell illustrated in FIG. 3;

FIG. 6 is a flowchart illustrating a method of manufacturing a solarcell according to another embodiment of the present invention;

FIG. 7 is a sectional view illustrating another example of the solarcell, to which a post-treatment operation of the method of manufacturingthe solar cell according to the embodiment of the present invention maybe applied; and

FIG. 8 is a graph illustrating relative values of the density ofcharging of a plurality of solar cells manufactured according toExperimental Example 2 of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Reference will now be made in detail to the embodiments of the presentinvention, examples of which are illustrated in the accompanyingdrawings. However, it will be understood that the present inventionshould not be limited to the embodiments and may be modified in variousways.

In the drawings, to clearly and briefly explain the present invention,illustration of elements having no connection with the description isomitted, and the same or extremely similar elements are designated bythe same reference numerals throughout the specification. In addition,in the drawings, for more clear explanation, the dimensions of elements,such as thickness, width, and the like, are exaggerated or reduced, andthus the thickness, width, and the like of the present invention are notlimited to the illustration of the drawings.

In the entire specification, when an element is referred to as“including” another element, the element should not be understood asexcluding other elements so long as there is no special conflictingdescription, and the element may include at least one other element. Inaddition, it will be understood that, when an element such as a layer,film, region or substrate is referred to as being “on” another element,it can be directly on the other element or intervening elements may alsobe present. On the other hand, when an element such as a layer, film,region or substrate is referred to as being “directly on” anotherelement, this means that there are no intervening elements therebetween.

Hereinafter, a method of manufacturing a solar cell according to anembodiment of the present invention will be described in detail withreference to the accompanying drawings. An example of the solar cell, towhich the method of manufacturing the solar cell according to theembodiment of the present invention may be applied, will first bedescribed, and thereafter, the method of manufacturing the solar cell,which includes a post-treatment operation of performing post-treatmenton the solar cell, will be described.

FIG. 1 is a sectional view illustrating an example of the solar cell, towhich a method of manufacturing the solar cell according to anembodiment of the present invention may be applied.

Referring to FIG. 1, the solar cell 100 according to the presentembodiment includes a semiconductor substrate 110 including a base area10, tunneling films 52 and 54 formed on the semiconductor substrate 110,conductive areas 20 and 30 formed on the respective tunneling films 52and 54, and electrodes 42 and 44 connected to the respective conductiveareas 20 and 30. In this instance, the tunneling films 52 and 54 mayinclude a first tunneling film 52 formed on a first surface (hereinafterreferred to as a “front surface”) of the semiconductor substrate 110,and a second tunneling film 54 formed on a second surface (hereinafterreferred to as a “back surface”) of the semiconductor substrate 110. Theconductive areas 20 and 30 may include a first conductive area 20 formedon the first tunneling film 52 at the front surface side of thesemiconductor substrate 110, and a second conductive area 30 formed onthe second tunneling film 54 at the back surface side of thesemiconductor substrate 110. In addition, the electrodes 42 and 44 mayinclude a first electrode 42 connected to the first conductive area 20,and a second electrode 44 connected to the second conductive area 30.This will be described below in more detail.

The semiconductor substrate 110 may be formed of crystallinesemiconductors. In one example, the semiconductor substrate 110 may beformed of monocrystalline or polycrystalline semiconductors (e.g.monocrystalline or polycrystalline silicon). In particular, thesemiconductor substrate 110 may be formed of monocrystallinesemiconductors (e.g. a monocrystalline semiconductor wafer, and morespecifically, a monocrystalline silicon wafer). When the semiconductorsubstrate 110 is formed of monocrystalline semiconductors (e.g.monocrystalline silicon) as described above, the solar cell 100configures a monocrystalline semiconductor solar cell (e.g. amonocrystalline silicon solar cell). Such a solar cell 100, which isbased on the semiconductor substrate 160 formed of monocrystallinesemiconductors having high crystallinity and thus low defects, may haveexcellent electrical properties.

In the present embodiment, the semiconductor substrate 110 may includeonly the base area 10 without a separate doped area. When thesemiconductor substrate 110 includes no separate doped area, forexample, damage to the semiconductor substrate 110 and an increase inthe amount of defects of the semiconductor substrate 110, which may begenerated when forming the doped area, may be prevented, which may allowthe semiconductor substrate 110 to have an excellent passivationproperty. Thereby, surface recombination, which occurs on the surface ofthe semiconductor substrate 110, may be minimized.

In the present embodiment, the semiconductor substrate 110 or the basearea 10 may be doped with a first or second conductive dopant at a lowdoping density, thus being of a first or second conductive type. At thistime, the semiconductor substrate 110 or the base area 10 may have alower doping density, higher resistance, or lower carrier density thanone of the first and second conductive areas 20 and 30, which is of thesame conductive type as the semiconductor substrate 110 or the base area10. In one example, in the present embodiment, the base area 10 may beof a second conductive type.

The front surface and/or the back surface of the semiconductor substrate110 may be subjected to texturing so as to have protrusions. Theprotrusions may be configured as (111) faces of the semiconductorsubstrate 110 and may take the form of pyramids having irregular sizes.When the roughness of, for example, the front surface of thesemiconductor substrate 110 is increased by the protrusions formed onthe front surface via texturing, the reflectance of light introducedthrough, for example, the front surface of the semiconductor substrate110 may be reduced. Accordingly, the quantity of light, which reachesthe pn junction formed by the base area 10 and the first conductive area20, may be increased, which may minimize shading loss. However, theembodiments of the present invention are not limited thereto, and noprotrusions may be formed on the front surface and the back surface ofthe semiconductor substrate 110 via texturing.

The first tunneling film 52 is formed on the front surface of thesemiconductor substrate 110, and the second tunneling film 54 is formedon the back surface of the semiconductor substrate 110.

The first and second tunneling films 52 and 54 may serve as a barrierfor electrons and holes, thereby preventing minority carriers frompassing through the first and second tunneling films 52 and 54 andallowing only majority carriers, which accumulate at the portionsadjacent to the first and second tunneling films 52 and 54 and thus hasa given amount of energy or more, to pass through the first and secondtunneling film 52 and 54. At this time, the majority carriers, whichhave the given amount of energy or more, may easily pass through thefirst and second tunneling films 52 and 54 owing to tunneling effects.

Such a first or second tunneling film 52 or 54 may include variousmaterials to enable the tunneling of the carriers, and for example, mayinclude a nitride, semiconductor, or conductive polymer. In one example,the first or second tunneling film 52 or 54 may include a silicon oxide,silicon nitride, silicon oxide nitride, intrinsic amorphoussemiconductor (e.g. intrinsic amorphous silicon), or intrinsicpolycrystalline semiconductor (e.g. intrinsic polycrystalline silicon).At this time, the first and second tunneling films 52 and 54 may beformed of intrinsic amorphous semiconductor. In one example, the firstand second tunneling films 52 and 54 may be configured as an amorphoussilicon (a-Si) layer, an amorphous silicon carbide (a-SiCx) layer, or anamorphous silicon oxide (a-SiOx) layer. In this instance, because thefirst and second tunneling films 52 and 54 have properties similar tothose of the semiconductor substrate 110, the surface properties of thesemiconductor substrate 110 may be effectively improved.

At this time, the first and second tunneling films 52 and 54 may beformed over the entire front surface and the entire back surface of thesemiconductor substrate 110. Accordingly, the first and second tunnelingfilms 52 and 54 may provide the entire front surface and the entire backsurface of the semiconductor substrate 110 with passivation effects, andmay be easily formed without separate patterning.

In order to achieve sufficient tunneling effects, the thickness of thetunneling films 52 and 54 may be 5 nm or less, and may be within a rangefrom 0.5 nm to 5 nm (e.g. within a range from 1 nm to 4 nm). When thethickness of the tunneling films 52 and 54 exceeds 5 nm, smoothtunneling does not occur, and consequently, the solar cell 100 may notoperate. When the thickness of the tunneling films 52 and 54 is below0.5 nm, it may be difficult to form the tunneling films 52 and 54 havinga desired quality. Accordingly, in order to further improve tunnelingeffects, the thickness of the tunneling films 52 and 54 may be within arange from 1 nm to 4 nm. However, the embodiments of the presentinvention are not limited thereto, and the thickness of the tunnelingfilms 52 and 54 may have any of various values.

The first conductive area 20 of a first conductive type may be formed onthe first tunneling film 52. In addition, the second conductive area 30of a second conductive type, which is the opposite of the firstconductive type, may be formed on the second tunneling film 54.

The first conductive area 20 may include a first conductive dopant, andthus may be of a first conductive type. In addition, the secondconductive area 30 may include a second conductive dopant, and thus maybe of a second conductive type. In one example, the first conductivearea 20 may come into contact with the first tunneling film 52, and thesecond conductive area 30 may come into contact with the secondtunneling film 54. Thereby, the structure of the solar cell 100 may besimplified, and the tunneling effects of the first and second tunnelingfilms 52 and 54 may be maximized. However, the embodiments of thepresent invention are not limited thereto.

Each of the first and second conductive areas 20 and 30 may comprise thesame semiconductor material as the semiconductor substrate 110 (morespecifically, a single semiconductor material, for example, silicon). Inone example, each of the first and second conductive areas 20 and 30 maybe configured as an amorphous silicon (a-Si) layer, an amorphous siliconcarbide (a-SiCx) layer, or an amorphous silicon oxide (a-SiOx) layer.Thereby, the first and second conductive areas 20 and 30 may haveproperties similar to those of the semiconductor substrate 110, and thusmay minimize a difference in properties that may occur when theycomprise different semiconductor materials. However, because the firstand second conductive areas 20 and 30 are formed on the semiconductorsubstrate 110 separately from the semiconductor substrate 110, the firstand second conductive areas 20 and 30 may have a crystalline structuredifferent from that of the semiconductor substrate 110, in order to beeasily formed on the semiconductor substrate 110.

For example, each of the first and second conductive areas 20 and 30 maybe formed by doping amorphous semiconductors, which may be easilymanufactured via any of various methods, such as, for example,deposition, with a first or second conductive dopant. Thereby, the firstand second conductive areas 20 and 30 may be easily formed using asimplified process. At this time, when the first and second tunnelingfilms 52 and 54 are formed of intrinsic amorphous semiconductor (e.g.intrinsic amorphous silicon), the first and second conductive areas 20and 30 may have, for example, an excellent bonding property andexcellent electrical conductivity.

When the base area 10 is of a second conductive type, the firstconductive area 20, which is of a first conductive type, configures anemitter area, which is of a different conductive type from that of thebase area 10, and thus forms a pn junction with the base area 10. Inaddition, the second conductive area 30, which is of the same secondconductive type as that of the semiconductor substrate 110, configures aback-surface field (BSF) area, which forms a back-surface field and hasa higher doping density than the semiconductor substrate 110. Thereby,when the first conductive area 20, which configures the emitter area, islocated at the front surface side of the semiconductor substrate 110,the path of light for a pn junction may be minimized.

However, the embodiments of the present invention are not limitedthereto. In another example, when the base area 10 is of a firstconductive type, the first conductive area 20 configures a front-surfacefield area, and the second conductive area 30 configures an emitterarea.

A p-type dopant, which is used as the first or second conductive dopant,may be a group-III element, such as boron (B), aluminum (Al), gallium(Ga), or indium (In), and an n-type dopant may be a group-V element,such as phosphorus (P), arsenic (As), bismuth (Bi), or antimony (Sb).However, the embodiments of the present invention are not limitedthereto, and any of various dopants may be used as the first or secondconductive dopant.

When at least one of the first and second tunneling films 52 and 54 andthe first and second conductive areas 20 and 30, which constitute aphotoelectric converter, includes an amorphous semiconductor layer (e.g.an amorphous silicon layer), the solar cell 100 may be manufactured in asimplified manner, the semiconductor substrate 110 may have excellentproperties because it includes only the base area 10 without a dopedarea, and the reduction in the thickness of the expensive semiconductorsubstrate 110 may reduce the cost of manufacturing the solar cell 100.However, the amorphous semiconductor layer may have many defects at theinterface with the semiconductor substrate 110, which forms aheteroepitaxial junction, and may easily undergo deterioration inproperties at a high temperature, thus requiring the application of alow-temperature process. When such a low-temperature process is applied,however, there is a limitation on reduction in, for example, the contactresistance between the conductive areas 20 and 30 and the electrodes 42and 44. In consideration of this, in the solar cell 100 having thephotoelectric converter including an amorphous semiconductor layeraccording to the present embodiment, a post-treatment operation ST50(see FIG. 3), which may prevent deterioration of the amorphoussemiconductor layer and may prevent an increase in the contactresistance between the conductive areas 20 and 30 and the electrodes 42and 44, is performed. This will be described below in more detail withregard to the manufacturing method or the post-treatment method of thesolar cell 100.

The first and second electrodes 42 and 44 are disposed on the respectivefirst and second conductive areas 20 and 30 and are connected thereto.The first and second electrodes 42 and 44 may include the firstelectrode 42 disposed on and connected to the first conductive area 20,and the second electrode 44 disposed on and connected to the secondconductive area 30.

The first electrode 42 may include a first electrode layer 421 and asecond electrode layer 422, which are stacked over the first conductivearea 20 in sequence.

In this instance, the first electrode layer 421 may be formed over (e.g.may be in contact with) the entire first conductive area 20. The term“entire” includes not only the case where the entire first conductivearea 20 is covered without leaving an empty space or an empty area, butalso the case where a portion of the first conductive area 20 isinevitably excluded. When the first electrode layer 421 is formed overthe entire first conductive area 20, the carriers may easily reach thesecond electrode layer 422 by passing through the first electrode layer421, which may result in reduced resistance in the horizontal direction.Because the first conductive area 20, which is configured as anamorphous semiconductor layer, may have relatively low crystallinity,and thus may reduce the mobility of the carriers, the provision of thefirst electrode layer 421 may reduce resistance when the carriers movein the horizontal direction.

Because the first electrode layer 421 is formed over the entire firstconductive area 20, the first electrode layer 421 may be formed of amaterial capable of transmitting light (i.e. a light-transmittingmaterial). That is, the first electrode layer 421 may be formed of atransparent conductive material in order to enable the transmission oflight and the easy movement of the carriers. As such, the firstelectrode layer 421 does not prevent the transmission of light even ifit is formed over the entire first conductive area 20. In one example,the first electrode layer 421 may include an indium tin oxide (ITO) or acarbon nano tube (CNT). However, the embodiments of the presentinvention are not limited thereto, and the first electrode layer 421 mayinclude any of various other materials.

The second electrode layer 422 may be formed on the first electrodelayer 421. In one example, the second electrode layer 422 may come intocontact with the first electrode layer 421, which may simplify thestructure of the first electrode 42. However, the embodiments of thepresent invention are not limited thereto, and various alterations arepossible. For example, an alteration, in which a separate layer ispresent between the first electrode layer 421 and the second electrodelayer 422, is possible. Meanwhile, although the second electrode layer422 may have a single layer structure as illustrated, or may have amulti-layered structure unlike the illustration.

The second electrode layer 422, disposed on the first electrode layer421, may be formed of a material having electrical conductivity superiorto that of the first electrode layer 421. As such, the efficiency bywhich the second electrode layer 422 collects the carriers and thereduction in the resistance of the second electrode layer 422 may befurther enhanced. In one example, the second electrode layer 422 may beformed of a metal, which is opaque or has lower transparency than thefirst electrode layer 421 and has electrical conductivity superior tothat of the first electrode layer 421.

Because the second electrode layer 422 is opaque or has lowtransparency, and thus may prevent the entry of light, the secondelectrode layer 422 may have a given pattern so as to minimize shadingloss. This may allow light to be introduced into the portion at whichthe second electrode layer 422 is not formed. The plan shape of thesecond electrode layer 422 will be described below in more detail withreference to FIG. 2.

The second electrode 44 may include a first electrode layer 441 and asecond electrode layer 442, which are stacked over the second conductivearea 30 in sequence. The role, material, shape and the like of the firstand second electrode layers 441 and 442 of the second electrode 44 maybe the same as the role, material, shape and the like of the first andsecond electrode layers 421 and 422 of the first electrode 42 except forthe fact that the second electrode 44 is located on the secondconductive area 30, and therefore the description related to the firstelectrode 42 may be equally applied to the second electrode 44.

In addition, various layers, such as, for example, an anti-reflectionfilm and a reflection film, may be disposed on the first electrodelayers 421 and 441 of the first and second electrodes 42 and 44.

At this time, in the first and second electrodes 42 and 44 of in thepresent embodiment, the second electrode layers 422 and 442 may beformed of a material that may be fired by low-temperature firing (e.g.firing at a processing temperature of 300° C. or less). In one example,the second electrode layers 422 and 442 may not include (or lack) aglass frit, but may include only a conductive material and a resin (e.g.a binder, a curing agent, or an additive). This serves to allow thesecond electrode layers 422 and 442 having no glass frit to be easilyfired at a low temperature. The conductive material may include, forexample, silver (Ag), aluminum (Al), or copper (Cu), and the resin mayinclude, for example, a cellulose-based or phenolic-based binder, or anamine-based curing agent.

As described above, in the present embodiment, because the secondelectrode layers 422 and 442 need to be formed in contact with the firstelectrode layers 421 and 441, a fire-through that penetrates, forexample, an insulation film is not required. Accordingly,low-temperature firing paste, from which the glass frit is removed, isused. Because the second electrode layers 422 and 442 include only theresin without the glass frit, the conductive material may be subjectedto sintering so as to be brought into contact with the first conductivelayers 421 and 441 without being connected thereto, thereby achievingconductivity via aggregation. This conductivity may be low. Inconsideration of this, in the present embodiment, the post-treatmentoperation ST50 may be performed in order to enhance conductivity. Thiswill be described below in more detail with regard to the manufacturingmethod or the post-treatment method of the solar cell 100.

The plan shape of the second electrode layers 422 and 442 of the firstand second electrodes 42 and 44 will be described below in more detailwith reference to FIG. 2.

FIG. 2 is a plan view of the second electrode layers 422 and 442 in thesolar cell 100 illustrated in FIG. 1. The illustration of FIG. 2 isfocused on the second electrode layers 422 and 442 of the first andsecond electrodes 42 and 44.

Referring to FIG. 2, the first and second electrode layers 422 and 442may include a plurality of finger electrodes 42 a and 44 a spaced apartfrom one another at a constant pitch. While FIG. 2 illustrates that thefinger electrodes 42 a and 44 a are parallel to one another and areparallel to the edge of the semiconductor substrate 110, the embodimentsof the present invention are not limited thereto. In addition, thesecond electrode layers 422 and 442 may include bus-bar electrodes 42 band 44 b, which are formed in a direction crossing the finger electrodes42 a and 44 a so as to interconnect the finger electrodes 42 a and 44 a.Only one bus-bar electrode 42 b or 44 b may be provided, or a pluralityof bus-bar electrodes 42 b or 44 b may be arranged at a larger pitchthan the pitch of the finger electrodes 42 a and 44 a as illustrated inFIG. 2. At this time, although the width of the bus-bar electrodes 42 band 44 b may be larger than the width of the finger electrodes 42 a and44 a, the embodiments of the present invention are not limited thereto.Accordingly, the width of the bus-bar electrodes 42 b and 44 b may beequal to or less than the width of the finger electrodes 42 a and 44 a.

FIG. 2 illustrates that the second electrode layers 422 and 442 of thefirst electrode 42 and the second electrode 44 may have the same planshape. However, the embodiments of the present invention are not limitedthereto, and the width, pitch and the like of the finger electrodes 42 aand the bus-bar electrodes 42 b of the first electrode 42 may bedifferent from the width, pitch and the like of the finger electrodes 44a and the bus-bar electrodes 44 b of the second electrode 44. Inaddition, the second electrode layers 422 and 442 of the first electrode42 and the second electrode 44 may have different plan shapes, andvarious other alterations are possible.

As such, in the present embodiment, in the first and second electrodes42 and 44 of the solar cell 100, the second electrode layers 422 and442, which are opaque or comprises a metal, may have a predeterminedpattern so that the solar cell 100 has a bi-facial structure to allowlight to be introduced into the front surface and the back surface ofthe semiconductor substrate 110. Thereby, the quantity of light used inthe solar cell 100 may be increased, which may contribute to enhancementin the efficiency of the solar cell 100. However, the embodiments of thepresent invention are not limited thereto, and the second electrodelayer 442 of the second electrode 44 may be formed at the entire backsurface of the semiconductor substrate 110.

As described above, the solar cell 100, which has the photoelectricconverter including the amorphous semiconductor layer, may be subjectedto post-treatment, so as to prevent deterioration of the amorphoussemiconductor layers and to enhance the conductivity of the electrodes42 and 44. This will be described below in more detail with regard tothe manufacturing method of the solar cell 100.

FIG. 3 is a flowchart illustrating the manufacturing method of the solarcell according to an embodiment of the present invention, and FIGS. 4Ato 4I are sectional views illustrating the manufacturing method of thesolar cell illustrated in FIG. 3. Hereinafter, a detailed descriptionrelated to the configurations of the solar cell 100 described above withreference to FIGS. 1 and 2 will be omitted, and only configurations notdescribed above will be described in detail.

Referring to FIG. 3, the manufacturing method of the solar cell 100according to the present embodiment includes a semiconductor substratepreparing operation ST10, a tunneling film forming operation ST20, aconductive area forming operation ST30, an electrode forming operationST40, and a post-treatment operation T50. The electrode formingoperation ST40 includes a first electrode layer forming operation ST41,a first low-temperature paste layer forming operation ST42, a firstdrying operation ST43, a second low-temperature paste layer formingoperation ST44, and a second drying operation ST45, This will bedescribed below in detail with reference to FIGS. 4A to 41.

First, as illustrated in FIG. 4A, in the semiconductor substratepreparing operation ST10, the semiconductor substrate 110 including thebase area 10 is prepared.

Subsequently, as illustrated in FIG. 4B, in the tunneling film formingoperation ST20, the tunneling films 52 and 54 are formed over the entiresurface of the semiconductor substrate 110. More specifically, the firsttunneling film 52 is formed on the front surface of the semiconductorsubstrate 110, and the second tunneling film 54 is formed on the backsurface of the semiconductor substrate 110. Although the tunneling films52 and 54 are illustrated in FIG. 4B as being not formed on the sidesurface of the semiconductor substrate 110, the tunneling films 52 and54 may also be formed on the side surface of the semiconductor substrate110.

The tunneling films 52 and 54 may be formed via, for example, thermalgrowth or deposition (e.g. plasma enhanced chemical vapor deposition(PECVD) or atomic layer deposition (ALD)). However, the embodiments ofthe present invention are not limited thereto, and the tunneling films52 and 54 may be formed via various other methods.

Subsequently, as illustrated in FIG. 4C, in the conductive area formingoperation ST30, the conductive areas 20 and 30 are formed on thetunneling films 52 and 54. More specifically, the first conductive area20 may be formed on the first tunneling film 52, and the secondconductive area 30 may be formed on the second tunneling film 54.

The conductive areas 20 and 30 may be formed via, for example,deposition (e.g. PECVD or low pressure chemical vapor deposition(LPCVD)). A first conductive dopant or a second conductive dopant may beintroduced to a semiconductor layer, which forms the conductive area 20or 30, in the growth process of the semiconductor layer, or may be dopedafter the semiconductor layer is formed, via, for example,ion-implantation, thermal diffusion, or laser doping. However, theembodiments of the present invention are not limited thereto, and theconductive areas 20 and 30 may be formed via various other methods.

Subsequently, as illustrated in FIG. 4D, in the first electrode layerforming operation ST41, the first electrode layers 421 and 441 areformed respectively on the conductive areas 20 and 30. Morespecifically, the first electrode layer 421 of the first electrode 42may be formed on the first conductive area 20, and the first electrodelayer 441 of the second electrode 44 may be formed on the secondconductive area 30.

The first electrode layers 421 and 441 may be formed via, for example,deposition (e.g. PECVD or coating). However, the embodiments of thepresent invention are not limited thereto, and the first electrodelayers 421 and 441 may be formed via various other methods.

Subsequently, as illustrated in FIG. 4E, in the first low-temperaturepaste layer forming operation ST42, a first low-temperature paste layer422 a is formed on one of the conductive areas 20 and 30 (the firstconductive area 20 in FIG. 4E). The first low-temperature paste layer422 a may include a conductive material, a resin (e.g. a binder, acuring agent, and an additive), and a solvent. The constituent materialsof the conductive material and the resin have already been described,and thus a description thereof is omitted here. The solvent may be anyof various materials, and for example, may be an ether-based solvent. Atthis time, with respect to 100 wt % of the first low-temperature pastelayer 422 a, the conductive material may be included in an amount of 85wt % to 90 wt %, the resin may be included in an amount of 1 wt % to 15wt %, and the solvent may be included in an amount of 5 wt % to 10 wt %.However, the embodiments of the present invention are not limitedthereto.

The first low-temperature paste layer 422 a may be formed via variousmethods. In one example, the first low-temperature paste layer 422 a maybe formed to have a desired pattern via printing. As such, the firstlow-temperature paste layer 422 a may be formed into a desired patternvia a simplified process. Meanwhile, the first low-temperature pastelayer 422 a may have a single layer structure as illustrated, or mayhave a multi-layered structure unlike the illustration.

Subsequently, as illustrated in FIG. 4F, in the first drying operationST43, the first low-temperature paste layer 422 a is dried so that oneof the second electrode layers 422 and 442 (the second electrode layer422 of the first electrode 42 in FIG. 4F) is formed. The first dryingoperation ST43 may be performed at a temperature of 300° C. or less.This temperature is limited to a low temperature at which deteriorationof the tunneling films 52 and 54 and the conductive areas 20 and 30 maybe prevented. However, the embodiments of the present invention are notlimited thereto.

When the solvent of the first low-temperature paste layer 422 a isvolatilized in the first drying operation ST43, one of the secondelectrode layers 422 and 442 (the second electrode layer 422 of thefirst electrode 42 in FIG. 4F) includes the conductive material and theresin.

Subsequently, as illustrated in FIG. 4G, in the second low-temperaturepaste layer forming operation ST44, a second low-temperature paste layer442 a is formed on the other one of the conductive areas 20 and 30 (thesecond conductive area 30 in FIG. 4G). The second low-temperature pastelayer 442 a may include a conductive material, a binder, and a solvent.The second low-temperature paste layer 442 a may include, for example,the same or similar material or composition as the first low-temperaturepaste layer 422 a, and thus a detailed description thereof is omittedhere.

The second low-temperature paste layer 442 a may be formed via variousmethods. In one example, the second low-temperature paste layer 442 amay be formed to have a desired pattern via printing. As such, thesecond low-temperature paste layer 442 a may be formed into a desiredpattern via a simplified process.

Subsequently, as illustrated in FIG. 4H, in the second drying operationST45, the second low-temperature paste layer 442 a is dried so that theother one of the second electrode layers 422 and 442 (the secondelectrode layer 442 of the second electrode 44 in FIG. 4H) is formed.The second drying operation ST45 may be performed at the temperature of300° C. or less. This temperature is limited to a low temperature atwhich deterioration of the tunneling films 52 and 54 and the conductiveareas 20 and 30 may be prevented. However, the embodiments of thepresent invention are not limited thereto.

When the solvent of the second low-temperature paste layer 442 a isvolatilized in the second drying operation ST45, the other one of thesecond electrode layers 422 and 442 (the second electrode layer 442 ofthe second electrode 44 in FIG. 4H) includes the conductive material andthe resin, without including a metal compound, which includes, forexample, oxygen, carbon, and sulfur.

In the drawings and the above description, after the firstlow-temperature paste layer 422 a is formed and dried, the secondlow-temperature paste layer 442 a is formed and dried. It may bedifficult to form the first and second low-temperature paste layers 422a and 442 a, which are in a liquid state, on opposite surfaces such thatthey both have the desired pattern at the same time. In consideration ofthis, in the state in which one of the second electrode layers 422 and442 has been formed by forming and drying the first low-temperaturepaste layer 422 a, which is in a liquid state, the secondlow-temperature paste layer 442 a, which is in a liquid state, is formedon the opposite surface. Thereby, it is possible to prevent, forexample, the first low-temperature paste layer 422 a from flowing downwhile the second low-temperature paste layer 442 a is formed. However,the embodiments of the present invention are not limited thereto, andthe first and second low-temperature paste layers 422 a and 442 a may beformed on opposite sides at the same time, and thereafter may be driedtogether.

In the drawings and the above description, after the firstlow-temperature paste layer 422 a has been formed and dried on the firstconductive area 20, which is disposed on the front surface of thesemiconductor substrate 110, the second electrode layer 422 of the firstelectrode 42 is formed. Thereafter, after the second low-temperaturepaste layer 442 a has been formed and dried on the second conductivearea 30, which is disposed on the back surface of the semiconductorsubstrate 110, the second electrode layer 442 of the second electrode 44is formed. However, this sequence is given only by way of example, andthe embodiments of the present invention are not limited thereto. Afterthe first low-temperature paste layer 422 a has been formed and dried onthe second conductive area 30, which is disposed on the back surface ofthe semiconductor substrate 110, the second electrode layer 442 of thesecond electrode 44 may be formed. At this time, the secondlow-temperature paste layer 442 a, which is formed after the firstlow-temperature paste layer 422 a, may be formed and dried on the firstconductive area 20, which is disposed on the front surface of thesemiconductor substrate 110, so as to form the second electrode layer422 of the first electrode 42.

Subsequently, as illustrated in FIG. 4I, the post-treatment operationST50 for providing the solar cell 100 with light is performed. At thistime, when heat is also provided to the solar cell 100, the effect ofthe post-treatment operation ST50 may be further improved. Meanwhile, inthe present embodiment, the post-treatment operation ST50 may be atwo-operation post-treatment. This will be described later.

When light is provided to the solar cell 100 in the post-treatmentoperation ST50, the mobility of hydrogen is improved and the diffusionrate of hydrogen is increased. In the case where the tunneling films 52and 54 and/or the conductive areas 20 and 30 are configured as amorphoussemiconductor layers, a great amount of hydrogen is included therein.When the diffusion rate of hydrogen is increased, hydrogen may easilydiffuse to the interfaces therebetween. Thereby, the amount of hydrogeninside the amorphous semiconductor layers may be greatly reduced, andthe incidence of defects in the interfaces may be reduced.

In this way, it is possible to prevent deterioration of the amorphoussemiconductor layers, which may occur when the reactivity of hydrogeninside the amorphous semiconductor layers increases due to light orheat. Accordingly, the thermal stability of the solar cell 100 may besecured at a temperature of 200° C. or more. In one example, the solarcell 100, manufactured by the manufacturing method according to thepresent embodiment, may have thermal stability at a temperature of 300°C. or less. Thereby, deterioration of the amorphous semiconductor layersmay be prevented in a subsequent module process, such as, for example, aprocess of attaching ribbons to the solar cell 100. In addition,reduction in the defects in the interfaces may improve passivationeffects.

The method of manufacturing the solar cell according to the presentinvention may be performed at a relatively low temperature, i.e. aprocessing temperature of 300° C. or less. Thus, because the process ofmanufacturing the solar cell 100 is not performed at a high processingtemperature (e.g. a temperature above 300° C.), deterioration of thesemiconductor layers included in the solar cell 100 may be preventedduring the manufacturing operations of the solar cell 100.

In addition, the conductivity of the electrodes 42 and 44 formed usingthe first and second low-temperature paste layers 422 a and 442 a may beenhanced by the light provided in the post-treatment operation ST50. Itis expected that this is because light increases the activity of abinder included in the first and second low-temperature paste layers 422a and 442 a, thus exerting light-sintering effects.

At this time, the light, provided to the solar cell 100 in thepost-treatment operation ST50, may have luminous intensity with a rangefrom 100 W/m² to 30000 W/m². When the luminous intensity is below 100W/m², the effect of the post-treatment operation ST50 may beinsufficient. On the other hand, it may be difficult to realize lighthaving luminous intensity above 30000 W/m² using current light sources.In one example, the light provided to the solar cell 100 in thepost-treatment operation ST50 may have luminous intensity within a rangefrom 100 W/m² to 20000 W/m². Thereby, the effect of the post-treatmentoperation ST50 may be effectively improved.

In one example, the light provided to the solar cell 100 in thepost-treatment operation ST50 may have a wavelength within a range from300 nm to 1000 nm. Infrared light, having a wavelength above 1000 nm,may heat the solar cell 100 to an uncontrollable level. Therefore, inthe present embodiment, the effect of the post-treatment operation ST50of the solar cell 100 may be maximized using only light, which has awavelength associated with only the post-treatment of the solar cell100. In one example, the light provided to the solar cell 100 may have awavelength within a range from 400 nm to 800 nm. When deterioration ofthe amorphous semiconductor layers is prevented using light having awavelength that is directly involved in the photoelectric conversion ofthe solar cell 100, the effect of the post-treatment operation ST50 ofthe solar cell 100 may be maximized.

Meanwhile, the light, provided to the solar cell 100 in thepost-treatment operation ST50, may have a wavelength of 400 nm or less,and specifically, may have a wavelength within a range from 300 nm to400 nm. In this instance, the luminous intensity may range from 100 W/m²to 5000 W/m². In addition, the light provided to the solar cell 100 inthe post-treatment operation ST50 may have a wavelength that exceeds 400nm and is equal to or less than 1000 nm. In this case, the luminousintensity may range from 100 W/m² to 30000 W/m². This is because thelight provided to the solar cell 100 has different energies depending onthe wavelength thereof, and thus the luminous intensity may vary tocorrespond to the wavelengths of light.

Accordingly, because light having a wavelength of 400 nm or less hashigh energy, the effect may be maximized by providing lower luminousintensity than light having a wavelength above 400 nm. As such, thelight provided to the solar cell 100 in the post-treatment operationST50 may facilitate the firing of the first and second low-temperaturepaste layers 422 a and 442 a at a wavelength and luminous intensitywithin the above-described ranges, and may prevent deterioration of theamorphous semiconductor layers by light owing to the increased mobilityof hydrogen. In the present embodiment, the post-treatment operationST50 may be performed at room temperature or in the state in which heatis applied. In particular, the firing of the first and secondlow-temperature paste layers 422 a and 442 a may be facilitated whenheat and light are provided together in the post-treatment operationST50. In addition, when the mobility of hydrogen is improved,deterioration of the amorphous semiconductor layers by light may beprevented. In one example, the processing temperature in thepost-treatment operation ST50 may be room temperature or 300° C. (e.g.within a range from 15° C. to 300° C.). In this instance, the processingtemperature may mean the temperature of the solar cell 100 (or thesemiconductor substrate 110) on which the post-treatment operation ST50is performed. When the processing temperature is lower than roomtemperature, the effect of the post-treatment operation ST50 may bereduced and an additional device may be required in order to realize atemperature that is lower than room temperature. When the processingtemperature exceeds 300° C., the amorphous semiconductor layers may bedeteriorated while the post-treatment operation ST50 is performed, priorto realizing the effect of the post-treatment operation ST50. In oneexample, the processing temperature in the post-treatment operation ST50may range from 100° C. to 300° C. This is because the effect of thepost-treatment operation ST50 may be further enhanced when theprocessing temperature is 100° C. or more.

At this time, in the present embodiment, the processing temperature inthe post-treatment operation ST50 may range from 200° C. to 300° C. Thisis because, as described above, according to the present invention, thelight applied in the post-treatment operation ST50 may preventdeterioration of the amorphous semiconductor layers in the solar cell100, and thus the thermal stability of the solar cell 100 may be securedat a temperature of 200° C. or more. As such, the post-treatmentoperation ST50 may be performed at a relatively high processingtemperature within a range from 200° C. to 300° C. This may minimize theresistance of the amorphous semiconductor layers and may greatly enhancethe specific resistance of the electrodes 42 and 44. In addition, in thepresent embodiment, the temperature of the solar cell 100, i.e. theprocessing temperature in the post-treatment operation ST50, may beeffectively increased by light. That is, when heat and light are usedtogether, as illustrated in FIG. 5, the temperature of the solar cell100 may be increased by the light. Thereby, the amount of heat to besupplied to the solar cell 100 via a heat source may be reduced, whichmay reduce manufacturing costs. In addition, considering the fact thatit may be difficult to precisely control the temperature of the solarcell 100 using the heat applied from the heat source, when light isemitted in the state in which the temperature of the solar cell 100 ismade by the heat source to fall within an approximate temperature range,the temperature of the solar cell 100 may be precisely controlled to andstably maintained within the desired range.

In the present embodiment, the post-treatment operation ST50 may beperformed by introducing the solar cell 100 into a post-treatmentapparatus 200, which is maintained at the above-described processingtemperature and provides light, without a separate preheating process.This is because the processing temperature is not high, and thus at theprocessing temperature there is a low likelihood that, for example, theproperties of the solar cell 100 will be deteriorated due to rapidvariation in temperature. As such, a preheating process and a facilityfor the same may be eliminated, which may increase productivity.

The processing time of the post-treatment operation ST50 may range from30 seconds to 1 hour. When the processing time is below 30 seconds, theeffect of the post-treatment operation ST50 may be insufficient. Whenthe processing time exceeds 1 hour, the processing time is excessivelylong, thus causing reduced productivity. In one example, the processingtime of the post-treatment operation ST50 may range from 1 minute to 30minutes. As such, the effect of the post-treatment operation ST50 may bestably realized and high productivity may be maintained.

In one example, the solar cell 100 may be subjected to post-treatmentwithin the post-treatment apparatus 200, which includes a light sourceunit 222 for providing the solar cell 100 with light. At this time, thepost-treatment apparatus 200 may be a heat-treatment apparatus, whichfurther includes a heat source unit 224.

The light source unit 222 serves to provide the solar cell 100 withlight having desired luminous intensity. Because the luminous intensityof the light required in the post-treatment operation ST50 ranges from100 W/m² to 30000 W/m², the light source unit 222 may provide lighthaving luminous intensity within a range from 100 W/m² to 30000 W/m².

At this time, various methods of adjusting the luminous intensity of thelight source unit 222 may be applied in order to provide light havingluminous intensity required in the post-treatment operation ST50. Thatis, for example, the number, type, and output of light sources 222 a and222 b, which constitute the light source unit 222, may be adjusted, orthe distance between the light sources 222 a and 222 b and the solarcell 100 may be changed.

In the present embodiment, the light source unit 222 may include themultiple light sources 222 a and 222 b so as to provide the solar cell100 with sufficient light. However, the embodiments of the presentinvention are not limited thereto, and only one of the light sources 222a and 222 b may be provided when light having high luminous intensity isnot required.

In the present embodiment, each of the light sources 222 a and 222 b mayconfigure a Plasma Lighting System (PLS) that provides light via plasmalight emission. In the plasma lighting system, electromagnetic waves,such as microwaves, or incident beams, generated by a magnetron, areapplied to a particular gas charged inside a bulb so as to ionize thegas inside the bulb to a high degree (i.e. to generate plasma), thuscausing light to be emitted from the plasma. The wavelength of the lightemitted from the plasma lighting system may range from 300 nm to 1200nm.

The plasma lighting system does not use an electrode, a filament, ormercury, which are constituent elements of a conventional lightingsystem, and thus is eco-friendly and has a semi-permanent lifespan. Inaddition, the plasma lighting system has a very excellent maintenancerate of super luminous flux, thus having low variation in the quantityof light even after it has been used for a long time. Because the plasmalighting system is highly resistant to heat and thus has excellentthermal stability, the plasma lighting system may be used along with theheat source unit 224 in the same space without any problems, and mayemit light having sufficient luminous intensity. For reference, otherlight sources, such as, for example, light-emitting diodes, arevulnerable to heat, and thus have difficulty in being used along withthe heat source unit 224, and emit only light having a low level ofluminous intensity. In addition, the plasma lighting system may emitalmost continuously uniform light across the entire wavelength band ofvisible light, and thus may provide light similar to solar light. Atthis time, in the present embodiment, the gas, which is charged insidethe bulb of the plasma lighting system, may be an In—Br compound, whichis produced by combining indium (In) and bromine (Br) with each other.Thereby, the resulting light may have a spectrum that is more similar tosolar light than in the conventional case in which sulfur gas is used.When light having a similar spectrum to solar light is provided, thepost-treatment operation ST50 may be performed under conditions similarto solar light. Thereby, for example, deterioration due to solar lightmay be effectively preemptively prevented in the post-treatmentoperation ST50.

The present embodiment illustrates that the use of multiple lightsources 222 a and 222 b, which include the plasma lighting systems. Assuch, light having desired luminous intensity may be stably provided tothe solar cell 100. However, the embodiments of the present inventionare not limited thereto, and for example, xenon lamps, halogen lamps,lasers, or light-emitting diodes (LEDs) may be used as the light sources222 a and 222 b. That is, the light sources 222 a and 222 b may be atleast one of xenon lamps, halogen lamps, lasers, plasma lightingsystems, and light-emitting diodes (LEDs).

Meanwhile, UV lamps for emitting ultraviolet light may be used as thelight sources 222 a and 222 b. In this instance, the UV lamps may emitlight having a wavelength within a range from 300 nm to 400 nm. However,the embodiments of the present invention are not limited thereto, andthe UV lamp may emit extreme ultraviolet light having a wavelength below300 nm.

In the present embodiment, a cover substrate 223, which is located onthe front surface (i.e. the light-emitting surface) of each of the lightsources 222 a and 222 b, may include a base substrate 223 a, and aplurality of layers 223 b, which are disposed on the base substrate 223a and have different indices of refraction.

The base substrate 223 a may be formed of a material that has strengthcapable of protecting the light sources 222 a and 222 b and hastransmittance for enabling the transmission of light. For example, thebase substrate 223 a may be formed of glass.

The layers 223 b may be formed by stacking layers having differentindices of refraction one above another, and may serve as a filter forblocking undesired light. For example, the layers 223 b may be formed ofoxide-based materials having different indices of refraction, and mayblock light having a wavelength that is below 300 nm (e.g. below 600 nm)and exceeds 1200 nm (e.g. exceeds 1000 nm). The constituent materialsand the stacking structure of the layers 223 b may be selected fromamong various materials and various stacking structures, which may blocklight having a wavelength that is below 300 nm (e.g. below 600 nm) andexceeds 1200 nm (e.g. exceeds 1000 nm).

Although FIG. 4I illustrates that the layers 223 b are located on theouter surface of the base substrate 223 a, the embodiments of thepresent invention are not limited thereto. Thus, the layers 223 b may belocated on the inner surface of the base substrate 223 a, or may belocated on the inner and outer surfaces of the base substrate 223 a.

In the present embodiment, as a result of the cover substrate 223 of thelight source 222 a or 222 b blocking some of the light, an amount oflight that is sufficient for the post-treatment operation ST50 may beprovided to the solar cell 100. As such, the effect of thepost-treatment operation ST50 may be maximized while having a simplifiedstructure. However, the embodiments of the present invention are notlimited thereto, and for example, an optical filter installed betweenthe light sources 222 a and 222 b and the solar cell 100 may be used toblock some of the light, in addition to the cover plate 223 of the lightsources 222 a and 222 b.

The heat source unit 224 provides appropriate heat to allow the solarcell 100 to have a desired temperature in the post-treatment apparatus200. At this time, the heat source unit 224 may employ various types,structures, and shapes.

In one example, heat sources, which constitute the heat source unit 224,may be ultraviolet lamps, and for example, may be halogen lamps.Alternatively, for example, coil heaters may be used as the heatsources. When the heat sources use ultraviolet lamps, such as, forexample, halogen lamps, the temperature may be rapidly increasedcompared to the case where coil heaters are used. When the heat sourcesinclude coil heaters, facility costs may be reduced.

In the present embodiment, the heat source unit 224 may be spaced apartfrom the solar cell 100, or from a conveyor belt or a working table 204on which the solar cell 100 is placed, and may heat the solar cell 100via an atmospheric heating method that heats the atmosphere of a mainarea by radiation. Thereby, damage to the solar cell 100 by the heatsource unit 224 or problems, such as, for example, excessive heatemission to local portions of the solar cell 100 may be minimized. Forexample, when the heat sources of the heat source unit 224 areultraviolet lamps, the passivation properties of the passivation films22 and 32 may be deteriorated when ultraviolet light is directlyradiated thereon. In addition, when the heat sources of the heat sourceunit 224 come into contact with the solar cell 100 and thus cause, forexample, process errors, the solar cell 100 may be locally heated, whichmay cause problems, such as, for example, heating of a portion of thesolar cell 100 to an undesired temperature. However, the embodiments ofthe present invention are not limited thereto, and the solar cell 100may be heated by, for example, conduction, instead of the atmosphericheating method.

As described above, in the post-treatment operation ST50, light may beprovided by the light source unit 222, and a constant temperature may bemaintained by the heat source unit 224. At this time, in the presentembodiment, heat and light are provided to the solar cell 100 by thelight source unit 222 and the heat source unit 224, which are spacedapart from each other. That is, the light sources 222 a and 222 b, whichconstitute the light source unit 222, may be located together, and thelight sources 222 a and 222 b of the light source unit 222 are notinterspersed with the heat source unit 224. In this state, the lightsource unit 222 and the heat source unit 224 are adapted to separatelyprovide the solar cell 100 with light and heat, which may minimize theeffect of the light source unit 222 and the heat source unit 224 on eachother.

In one example, the light source unit 222 may be located on one side ofthe solar cell 100 and the heat source unit 224 may be located on theother side of the solar cell 100 in the main area. As such, light andheat from the light source unit 222 and the heat source unit 224 may beeffectively transferred to the solar cell 100, and interferencetherebetween may be minimized.

For example, the light source unit 222 may be located at the upper sideof the solar cell 100 (i.e. above the conveyor belt or the working table204), and the heat source unit 224 may be located at the lower side ofthe solar cell 100 (i.e. beneath the conveyor belt or the working table204). When the light source unit 222 is located at the lower side of theconveyor belt or the working table 204, some of the light provided fromthe light source unit 222 may be blocked by the conveyor belt or theworking table 204, which may prevent the effective radiation of light.In contrast, the heat source unit 224 may provide the solar cell 100with sufficient heat via atmospheric heating or conduction even if it islocated at the lower side of the conveyor belt or the working table 204.Accordingly, in the present embodiment, the light source unit 222 may belocated at the upper side of the solar cell 100, or above the conveyorbelt or the working table 204, and the heat source unit 224 may belocated at the lower side of the solar cell 100, or beneath the conveyorbelt or the working table 204. However, the embodiments of the presentinvention are not limited thereto, and the exact positions of the lightsource unit 222 and the heat source unit 224 may be changed.

In the present embodiment, the solar cell 100 may be subjected topost-treatment in the post-treatment apparatus 200, which has anindependent batch structure. As such, external interference may beminimized during processing, which may maximize processing effects andmay enhance the uniformity of processing. In addition, a conveyor beltmay be omitted, which may reduce the cost of facilities. The solar cell100 may be subjected to post-treatment in the post-treatment apparatus200 via an inline process using, for example, a conveyor belt. As such,the post-treatment of the solar cell 100 may be performed at a highspeed, and the production of the solar cell 100 may be increased.

FIGS. 3 and 4A to 41 illustrate that the second drying operation ST45and the post-treatment ST50 are performed in separate processes.However, the embodiments of the present invention are not limitedthereto, and the second drying operation ST45 may be performed in thepost-treatment apparatus 200, whereby the second drying operation ST45and the post-treatment operation ST50 may be performed at the same time,as illustrated in FIG. 6. Thereby, the effect of the post-treatmentoperation ST50 may be realized through a simplified process without anadditional process.

When heat treatment is again performed on the solar cell 100 at a hightemperature after the post-treatment operation ST50, the effect of thepost-treatment operation ST50 may be reduced or eliminated. Therefore,the post-treatment operation ST50 may be performed during the latterhalf of the method of manufacturing the solar cell 100, and may beperformed simultaneously with or after the second drying operation ST45,which is performed at a relatively high temperature. This may preventreduction or elimination of the effect of the post-treatment operationST50.

Meanwhile, in the present invention, the post-treatment operation ST50may include two operations as described above. FIG. 4J is a diagram forexplaining the post-treatment operation ST50 including two operationsaccording to the present embodiment.

Considering FIG. 4J, the post-treatment operation ST50 may include afirst operation 1st operation and a second operation 2nd operation. Thefirst operation 1st operation may be an operation of supplying only heatvia a heater, and the second operation 2nd operation may be an operationof supplying heat and light at the same time using the heater and thelight source unit 222. Meanwhile, in the present embodiment, althoughthe temperature of the second operation 2nd operation is illustrated asbeing higher than the temperature of the first operation 1st operation,the technical sprit of the embodiments of the present invention are notlimited thereto. This illustration serves to explain that, when lightand heat are supplied together in the second operation 2nd operation,the temperature range in which deterioration of the solar cell 100 doesnot occur in the post-treatment operation ST50 may be raised compared tothe first operation 1st operation. Thus, the temperatures of the firstoperation 1st operation and the second operation 2nd operation may bethe same.

Referring again to FIG. 4J, the first operation 1st operation may beperformed at a temperature of 200° C. or less. When heat is provided tothe solar cell 100, the mobility of hydrogen may be improved and thediffusion rate of hydrogen may be increased. That is, in the case wherethe tunneling films 52 and 54 and/or the conductive areas 20 and 30 areconfigured as amorphous semiconductor layers, a great amount of hydrogenis included therein. When the diffusion rate of hydrogen is increased,hydrogen may easily diffuse to the interfaces therebetween. Thereby, theamount of hydrogen inside the amorphous semiconductor layers may begreatly reduced, and the incidence of defects in the interfaces may bereduced.

Subsequently, in the second operation 2nd operation, light isadditionally supplied using the light source unit 222. When heat andlight are provided together to the solar cell 100 in the secondoperation 2nd operation, the mobility of hydrogen may be improvedcompared to that in the first operation 1st operation, causing thediffusion rate of hydrogen to be increased. In addition, theconductivity of the electrodes 42 and 44 formed using the first andsecond low-temperature paste layers 422 a and 442 a may be enhanced. Itis expected that this is because light increases the activity of abinder included in the first and second low-temperature paste layers 422a and 442 a, thus exerting light-sintering effects. The light suppliedin the second operation 2nd operation may be substantially the same asthat described above with reference to FIG. 4I.

In the present embodiment, the first operation 1st operation and thesecond operation 2nd operation may be successively performed using aconveyor belt on which the solar cell 100 is placed, without limitationthereto, and may be separately performed.

In the present embodiment, in the second operation 2nd operation, thetemperature at which the solar cell 100 is deteriorated may be raisedbecause light is supplied. In the manufacture of the solar cell 100,when the solar cell 100 includes an amorphous semiconductor layer andthe processing temperature of the post-treatment operation ST50 exceeds200° C., the amorphous semiconductor layer may be deteriorated. However,when the processing temperature is low, the diffusion rate of hydrogenmay be reduced.

Therefore, the post-treatment operation ST50 according to the presentembodiment may raise the processing temperature to 200° C. or more usingthe second operation 2nd operation when the solar cell 100 includes anamorphous semiconductor layer. That is, deterioration of the solar cell100 may be prevented and the diffusion rate of hydrogen may be increasedby the second operation 2nd operation of the post-treatment operationST50 according to the present embodiment.

As described above with reference to FIGS. 41 and 4J, in the method ofmanufacturing the solar cell 100 according to the present embodiment,light may be provided to the solar cell 100 in the post-treatmentoperation ST50, which may reduce the amount of hydrogen included inamorphous semiconductor layers and may reduce the incidence of defectsin interfaces of the amorphous semiconductor layers. At this time, whenheat is also provided, the aforementioned effects may be furtherenhanced. Thereby, deterioration of the amorphous semiconductor layersmay be effectively prevented. In one example, the solar cell 100,manufactured by the method of the present embodiment, may acquirethermal stability at a temperature of 300° C. or less. On the otherhand, when the post-treatment operation ST50 is not performed on thesolar cell 100, the solar cell 100 may have very low thermal stabilityat a temperature of 200° C. or more, and thus the amorphoussemiconductor layers thereof may be easily deteriorated. In addition,the conductivity of the electrodes 42 and 44 may be enhanced. Thereby,for example, the density of charging of the solar cell 100 may beenhanced, resulting in enhanced efficiency of the solar cell 100.

The above-described embodiment illustrates that the post-treatmentoperation ST50 according to the present embodiment is performed on thesolar cell 100, which includes, as a photoelectric converter, not onlythe semiconductor substrate 110, but also the amorphous semiconductorlayers, i.e. the first and second tunneling films 52 and 54 and thefirst and second conductive areas 20 and 30. However, the embodiments ofthe present invention are not limited thereto. Thus, the post-treatmentoperation ST50 according to the present embodiment may be performed onthe solar cell 100 that has any of various structures including theamorphous semiconductor layers.

In one example, as illustrated in FIG. 7, the post-treatment operationST50 according to the present embodiment may also be performed on athin-film amorphous solar cell 300.

Referring to FIG. 7, the thin-film amorphous solar cell 300 according tothe present embodiment includes a first substrate 310 (hereinafterreferred to as a “front substrate”), and a first electrode 320, aphotoelectric converter 330, and a second electrode 340, which areformed on the front substrate 310 (more specifically, on the lowersurface of the front substrate 310 in FIG. 7). A sealing member 350 anda second substrate 360 (hereinafter referred to as a “back substrate”)may further be formed on the second electrode 340. At this time, thephotoelectric converter 330 includes a plurality of unit cells 330 a,330 b and 330 c, which are separated from one another by a firstseparator 322, a second separator 332, and a third separator 342, whilebeing electrically connected to one another.

In one example, the front substrate 310 may be a transparent substrateformed of, for example, glass or polymers.

The first electrode 320 may be formed of a transparent conductivematerial, which has light transmittance and electrical conductivity. Inone example, the first electrode 320 may be formed of a zinc oxide(ZnO), an indium tin oxide (ITO), or a tin oxide (SnO₂), or may beformed of a metal oxide and one or more foreign substances (dopantmaterials or impurities) (e.g. boron (B), fluorine (F), or aluminum(Al)) added thereto.

The photoelectric converter 330 may be an amorphous semiconductor layer,and may include a first conductive semiconductor layer (e.g. a firstconductive silicon layer), an intrinsic semiconductor layer (e.g. anintrinsic silicon layer), and a second conductive layer (e.g. a secondconductive silicon layer) so as to have a pin junction structure.Various known materials, structures, etc. may be applied to the firstconductive semiconductor layer, the intrinsic semiconductor layer, andthe second conductive semiconductor layer of the pin junction structure,and thus a description thereof is omitted here.

The second electrode 340 may be formed of a material (e.g. a metalmaterial) that has reflectance and conductivity superior to those of thefirst electrode 320. In one example, the second electrode 340 mayinclude a single layer or multiple layers formed of silver, aluminum,gold, nickel, chrome, titanium, palladium, or alloys thereof.

The sealing member 350 may be formed of ethylene-vinyl acetate (EVA),poly-vinyl butyral (PVB), silicone, an ester-based resin, or anolefin-based resin.

The back substrate 360 may take the form of a substrate, a film, or asheet, and may be formed of, for example, glass or polymers.

In the method of manufacturing the thin-film amorphous solar cell 300according to the present embodiment, the post-treatment operation ST50may be performed after at least the first electrode 320, thephotoelectric converter 330, and the second electrode 340 are formed onthe front substrate 310. Thereby, deterioration in the properties of thephotoelectric converter 330, which includes the amorphous semiconductorlayers (e.g. the amorphous silicon layers), may be prevented, and theconductivity of the second electrode 340, which is connected to thephotoelectric converter 330, may be enhanced.

Hereinafter, the present invention will be described in more detail withreference to experimental examples. The following experimental examplesare suggested in order to describe the present invention in more detail,and the embodiments of the present invention are not limited thereto.

Experimental Example 1

A solar cell having the structure illustrated in FIG. 1 was manufacturedby forming first and second tunneling films and first and secondconductive areas, configured as amorphous silicon layers, on acrystalline silicon substrate, forming a first low-temperature pastelayer and then performing a first drying operation, and forming a secondlow-temperature paste layer and then performing a second dryingoperation. At this time, the first and second low-temperature pastelayers were formed of paste including 90 wt % silver (Ag), 5 wt % of abinder, and 5 wt % of a solvent.

Subsequently, a post-treatment operation was performed by providing eachof a plurality of solar cells with light having luminous intensity ofabout 0 w/m² (or natural light without the provision of separate light),light having luminous intensity of about 800 w/m², and light havingluminous intensity of 10000 w/m² for 20 minutes. At this time, theprocessing temperature was maintained at about 100° C. In this instance,it could be found from experimentation results that, assuming that thedensity of charging is 1 when the luminous intensity is 0 w/m², therelative value of the density of charging was about 1.03 when theluminous intensity was about 800 w/m², and the relative value of thedensity of charging was about 1.07 when the luminous intensity was about10000 w/m².

That is, it can be appreciated that the density of charging when lightis used in the post-treatment operation is higher than the density ofcharging when light is not used in the post-treatment operation.

Accordingly, it can be appreciated that the density of charging of thesolar cell may be enhanced by the post-treatment operation in whichlight is supplied.

Experimental Example 2

A solar cell having the structure illustrated in FIG. 1 was manufacturedin a plural number by forming first and second tunneling films and firstand second conductive areas, configured as amorphous silicon layers, ona crystalline silicon substrate, forming a first low-temperature pastelayer and then performing a second drying operation, and forming asecond low-temperature paste layer and then performing a second dryingoperation. This is referred to as a solar cell according to Example 1.

A solar cell was manufactured in a plural number by forming first andsecond tunneling films and first and second conductive areas, configuredas amorphous silicon layers, on a crystalline silicon substrate, forminga first low-temperature paste layer and then performing a first dryingoperation, and forming a second low-temperature paste layer, butperforming no second drying operation illustrated in FIG. 4G. This isreferred to as a solar cell according to Example 2.

At this time, the first and second low-temperature paste layers wereformed of paste including 90 wt % silver (Ag), 5 wt % of a binder, and 5wt % of a solvent.

Subsequently, a post-treatment operation was performed by providing thesolar cells according to Example 1 and Example 2 with light havingluminous intensity of about 2500 w/m² for 20 minutes. At this time, thepost-treatment operation was performed on each of the solar cellsaccording to Example 1 and the solar cells according to Example 2 atdifferent processing temperatures of about 20° C. (a room temperaturestate in which no heat is separately supplied), about 50° C., about 110°C., about 200° C., about 300° C., about 400° C., and about 500° C. Thedensities of charging of the solar cells according to Example 1 andExample 2 were measured after the post-treatment operation wasperformed, and the relative values thereof are illustrated in FIG. 8.

Referring to FIG. 8, it can be appreciated in the solar cells accordingto Example 1 that the density of charging when the post-treatmentoperation was performed at a temperature of 300° C. or less is higherthan the density of charging when the post-treatment operation wasperformed at a temperature above 300° C. In addition, it can beappreciated that the density of charging is higher when thepost-treatment operation was performed at temperatures within a rangefrom about 50° C. to about 300° C. in the state in which heat wasadditionally provided than that when the post-treatment operation wasperformed at room temperature of about 20° C. in the state in which noheat was additionally provided. In particular, it can be appreciatedthat the density of charging is very high when the post-treatmentoperation is performed at temperatures within a range from about 100° C.to about 300° C.

In addition, it can be appreciated that the density of charging ofExample 2 in which the post-treatment operation was performedsimultaneously with the second drying operation is generally higher thanthe density of charging of Example 1, in which the post-treatmentoperation was performed after the second drying operation was performed.Because the properties of the first and second low-temperature pastelayers may be somewhat deteriorated when the drying operation isrepeated, it is expected that the density of charging is higher inExample 2, in which an additional post-treatment operation is notperformed, as a result of minimizing the number of times the first andsecond low-temperature paste layers were dried.

As is apparent from the above description, according to the presentembodiment, when light is provided to a solar cell in a post-treatmentoperation, the amount of hydrogen included in amorphous semiconductorlayers may be reduced, and the incidence of defects in interfacestherebetween may be reduced. At this time, this effect may be furtherenhanced when heat is also supplied. Thereby, deterioration of theamorphous semiconductor layers may be effectively prevented. Inaddition, the conductivity of electrodes may be enhanced. In this way,the efficiency of the solar cell may be enhanced owing to, for exampleenhancement in the density of charging of the solar cell.

The above described features, configurations, effects, and the like areincluded in at least one of the embodiments of the present invention,and should not be limited to only one embodiment. In addition, thefeatures, configurations, effects, and the like as illustrated in eachembodiment may be implemented with regard to other embodiments as theyare combined with one another or modified by those skilled in the art.Thus, content related to these combinations and modifications should beconstrued as including in the scope and spirit of the invention asdisclosed in the accompanying claims.

What is claimed is:
 1. A method of manufacturing a solar cell, themethod comprising: forming a photoelectric converter including anamorphous semiconductor layer; forming an electrode connected to thephotoelectric converter; and performing a post-treatment by providinglight to the photoelectric converter and the electrode.
 2. The methodaccording to claim 1, wherein the photoelectric converter includes: asemiconductor substrate; a tunneling film located on the semiconductorsubstrate; and a conductive area located on the tunneling film, andwherein at least one of the tunneling film and the conductive area isconfigured as the amorphous semiconductor layer.
 3. The method accordingto claim 2, wherein the conductive area is configured as an amorphoussilicon layer, an amorphous silicon carbide layer, or an amorphoussilicon oxide layer, and including a p-type or n-type dopant, andwherein the tunneling film is configured as an intrinsic amorphoussilicon layer, an amorphous silicon carbide layer, or an amorphoussilicon oxide layer.
 4. The method according to claim 2, wherein theelectrode is formed over an entirety of the conductive area, andincludes a first electrode layer formed of a transparent conductivematerial and a second electrode layer formed on the first electrodelayer and having a pattern, and wherein the second electrode layer isformed by forming and drying a paste layer that includes a solvent, aconductive material, and a binder.
 5. The method according to claim 2,wherein the tunneling film includes a first tunneling film located on afirst surface of the semiconductor substrate, and a second tunnelingfilm located on a second surface of the semiconductor substrate, andwherein the conductive area includes a first conductive area located onthe first tunneling film, and a second conductive area located on thesecond tunneling film.
 6. The method according to claim 1, wherein, inthe performing of the post-treatment, heat is provided along with thelight.
 7. The method according to claim 1, wherein, in the performing ofthe post-treatment, the light has a luminous intensity within a rangefrom 100 W/m² to 30000 W/m².
 8. The method according to claim 7,wherein, in the performing of the post-treatment, the luminous intensityof the light is within a range from 100 W/m² to 20000 W/m².
 9. Themethod according to claim 1, wherein, in the performing of thepost-treatment, any one of a xenon lamp, a halogen lamp, a laser, aplasma lighting system (PLS), and a light-emitting diode (LED) is usedas a light source.
 10. The method according to claim 1, wherein, in theperforming of the post-treatment, a processing temperature is within arange from 15° C. to 300° C.
 11. The method according to claim 10,wherein, in the performing of the post-treatment, the processingtemperature is within a range from 100° C. to 300° C.
 12. The methodaccording to claim 11, wherein, in the performing of the post-treatment,the processing temperature is within a range from 200° C. to 300° C. 13.The method according to claim 1, wherein, in the performing of thepost-treatment, the light has a wavelength within a range from 300 nm to1000 nm.
 14. The method according to claim 13, wherein the wavelength ofthe light is within a range from 400 nm to 800 nm.
 15. The methodaccording to claim 1, wherein, in the performing of the post-treatment,a processing time is within a range from 30 seconds to 1 hour.
 16. Themethod according to claim 15, wherein, in the performing of thepost-treatment, the processing time is within a range from 1 minute to30 minutes.
 17. The method according to claim 1, wherein the performingof the post-treatment may be performed after the forming of theelectrode, or may be performed simultaneously with at least part of theforming of the electrode.
 18. The method according to claim 17, whereinthe forming of the electrode includes: forming a paste layer including asolvent, a conductive material, and a binder; and drying the paste layerso as to form an electrode layer including the conductive material andthe binder, and wherein the performing of the post-treatment may beperformed after or simultaneously with the drying.
 19. The methodaccording to claim 18, wherein the electrode includes a first electrodelayer formed over an entire conductive area using a transparentconductive material, and a second electrode layer formed on the firstelectrode layer and having a pattern, and wherein the second electrodelayer is formed by the forming of the paste layer and the drying. 20.The method according to claim 18, wherein the paste layer lacks a glassfrit.
 21. The method according to claim 1, wherein the post-treatmentincludes a first operation and a second operation, and wherein the firstoperation provides only heat, and the second operation provides heat andlight together.
 22. The method according to claim 21, wherein the heatprovided in the second operation has a temperature that is equal to orgreater than a temperature of the heat provided in the first operation.23. The method according to claim 1, wherein, in the performing thepost-treatment, the light has a wavelength that is equal to or less than400 nm or less and has a luminous intensity within a range from 100 W/m²to 5000 W/m².